-LRB- CNN -RRB- -- Paul Walker 's sudden death has left many in Hollywood nearly too stunned to speak .

As the news of his death spread on Saturday , some celebrities , including Lady Gaga and Alyssa Milano , tweeted their disbelief .

Adored for his work in the `` Fast & Furious '' movie franchise , Walker was in the midst of filming a seventh installment at the time of his death . Two of his co-stars in the blockbuster series , Ludacris and Tyrese , expressed their grief on social media .

`` I ca n't believe I 'm writing this , '' singer/actor Tyrese shared on Instagram , along with a photo of himself with the late star . `` My heart is hurting so bad no one can make me believe this is real Father God I pray that you send clarity over this cause I just do n't understand ... My heart hurts it 's broken no one can convince me that this is real ... . Prayer warriors please pray real hard for his only child , his daughter and family ... ''

Ludacris , meanwhile , remembered Walker for his `` humble spirit '' with a verse : `` Wherever you blessed your presence you always left a mark , we were like brothers & our birthdays are only 1 day apart , now You will forever hold a place in all of our hearts . ''

The 40-year-old actor , who rose to fame in 2001 's `` The Fast & The Furious '' after appearing in '90s hits `` She 's All That '' and `` Varsity Blues , '' died in a car accident . He 'd been attending a charity event for his organization , Reach Out Worldwide .

Throughout the industry , several are mourning the loss of a great friend and , by their account , giving humanitarian :

Tellingly , Walker 's passing was felt throughout the entertainment world , as even those outside of acting took a moment to reflect on the sobering death .

Walker 's next film , `` Hours , '' is scheduled to be released on December 13 .

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Actor Paul Walker died in a car crash Saturday

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Several in Hollywood were stunned by the news

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Stars took to social media to express their grief